Rotor for centrifugal stills



Sept. 19, 1950 K, McLEAN 1- A 2,523,042

ROTOR FOR CENTRiFUGAL STILLS Filed Feb. 21, 1947 IN VEN TOR. Ema K. MLE/M/ a: RUSSELL H- 11/55 Patented Sept. 19, 1950 "UNITED STATES PATENT orricr.

ROTOR FOR CENTRIFUGAL STILLS "Eric 'K. McLean and Russell H. Ives, Rochester,

-N. Y., assignors, by mesne assignments, to Eastman Kodak Oompany, Rochester, N. Y.,.a corporation of New Jersey Application February 21, 1947, Serial No. 7 30,126

3'Claims. (o1.2c2 2-05) This invention relates to animproved apparatus for vacuum distillation of thermally decomposable substances while in .the form of a thin film and particularly to a rotating vaporizing surface which will have uniform temperature.

It is .well known in the vacuum distillation art to subject thermally decomposable substances to vacuum distill-ation'while in the form of a thin film. In the centrifugal stills of the past this has been accomplished by introducing astream of work iliquid at a'point near the center of a rotating, heated, thin metal plate. Centrifugal force acting on'the liquid spread it out in a thin film .and the heattransfer from the metal plate to the liquid effected the vaporization of the lighter, easilyvaporizedconstituents. The liquid flowed rapidly to the periphery of the rotating platewhere the residuewas collected in gutters. See Hickman Patents 2,210,928; 2,308,008; 2,343;- 667; 2,349,431; and 2,408,639. Since the liquid was'in'contact with ahot sur'face'for a very short time thermal decomposition was reduced to a minimum. 'There was, however, some thermal decomposition as evidenced'by a loss of as much as 33% of the vitamin A when concentrating it from a fish liver oil in a centrifugal highvacuum unobstructed-path "still.

lT-his invention has for its object to avoid a portion of the decomposition which takes place in centrifugal highvacuum "unobstructed-path distillation. Another object is to provide an improvedvaporizing surface for a centrifugal, highvacuum, unobstructed-path still. A further object is to provide a vaporizing surface for a centrifugal, high-vacuum, unobstructed-path still in whic'h the surface temperatureis nearly uniform at all points. Another 'object'isto improve the state of the art; Other obje-cts'will' appear hereinafter.

These "and other objects are accomplished by our invention which includes Vacuum distillation apparatus wherein a rotatable vaporizing surface is constructedrin comparatively thick form of a metal of high .thermal conductivity. Comiparatively massive construction, for example, heavy construction considerably in excess of the scale required in ord'er "for the rotor to have sufficient structural strength to function without breakdowmprovides a metal heat-reservoir whichgives the rotor, or vaporizing surface, a more uniform surface temperature than is the case where a thin metal rotor -.is used. .By constructing the rotor of a metal of high thermal conductivity such as aluminum, copper, silver, gold, or magnesium, or various plated combinations of such 2 metals, a method is provided whereby any variation in rotor surface temperature is quickly erased by the flow of heat.

In the following description we have given several of the preferred embodiments of our invention but it is to be understood that these-are set forth for the-purpose of illustration and not inilimitation thereof.

In the accompanying drawing, wherein like numbers refer-to likeparts, we have illustrated several of the preferred embodiments of our invention wherein:

Fig. l is a partial top view of the rotorshown in-cross section in Fig. 2. Fig. 2 is a sectional viewof .a rotorused in a small centrifugal still. Fig. 3 is a sectional view of a cup-shaped rotor of a type used in a large centrifugal still.

Referring to Figs. 1, 2, and3, numeral Ill desig nates the flat .area on which work liquid (not shown) is introduced. Numeral 'll designates the area from which vaporization takes place. Numeral I2 designates the center hole which is used to secure the rotor to the shaft (not shown). on which it rotates.

In operation a rotor in a centrifugal still is rotated by a shaft attached at hole 12. The heating-element underneath the rotor is placed in operation. The liquid to be distilled is introduced at the flat area I0 and centrifugalv force drives it over 'the vaporizing area into collecting gutters.

In'thepast rotors were made of aluminum or steel spinnings. A thin sheet of metal Wasattached to a vwood or metal chuck of the shape desired for the rotor. The chuck was then. r0 tated and a tool held against the spinning metal until it conformedto the contours of the chuck. A very thin sheet of metal was used as it was easy to work into shape and offered less re-. sistance .tothe flow of heat from the heating element'located beneath the rotor.

With the use of rotors composed of aluminum or steel spinnings there was a loss of approxi mately 33% of the vitamin A when it was concentrated from fish liver oils. This loss was caused by thermal decomposition but it was thought that such a loss was inherent in the operation of the still.

We have produced a rotor which has reduced the vitamin loss caused by thermal decomposition to approximately 16%. We have done this by constructing the .rotor of massive metal of high thermal conductivity such as magnesium, aluminum, copper, silver, and gold. We have made our new rotors thicker and heavier than the spinnings formerly used. By this design the heat radiated from the electric heating element underneath the rotor to the rotor is spread evenly and quickly to the surface of the rotor. Local overheating of the rotor surface is restricted and thermal decomposition is thus reduced to a minimum.

The coeificient of thermal conductivity is usuually expressed as the B. t. u.s which will flow through a cubic foot of the metal in an hour where the temperature differential on two opposing sides is 1 F. The coefficient varies slightly at various temperatures. The following table of thermal conductivity coeflicients at 212 F. is

from the Chemical Engineers Handbook, John H. Perry, 2nd edition, page 949.

Aluminum 119 Copper 218 Silver 238 Gold 170 Magnesium 92 We have found that rotors constructed of metals in the above group are satisfactory. Where the coefficient of thermal conductivity of the metal of which the rotor is constructed is below the coeflicient for magnesium there is less opportunity for the heat to flow uniformly over the surface of the rotor, and thermal decomposition of the distilland increases. The higher the coefficient the more satisfactory the metal for use in rotor construction.

We have found that a thick rotor gives less thermal decomposition of distilland than a thin one. Performance improves with thickness but we have had satisfactory results from a thickness of as littleas. Above 1% in thickness the perfomance is still further improved but the added resistance to heat flow necessitates heating units of larger capacity thus increasing power costs.

Where extremely large rotors are used, e. g. 10 ft. diameter, the rotor thickness at the vaporizing surface will be as much as 1 /2 inches, that is, the ratio of the thickness to the diameter is 1/80. In a medium-size rotor, e. g. in diameter, we prefer to operate with a rotor thickness within the range of A;- that is, a thickness to a diameter ratio of from /120 to /eu.

The method of fabrication is not important. Castings and forgings are equally satisfactory and other methods of fabrication would produce suitable rotors. I

Combinations of metals of high thermal conductivity may be used. For example, copper is a very desirable material of construction but it has a destructive effect upon certain vitamins. Silver is a desirable material of construction but it is expensive. A rotor constructed of copper with a silver coating would be comparatively inexpensive and would have excellent performance characteristics.

Alloys may be used provided their coeiiicient of thermal conductivity is sufficiently high. An alloy with a coefficient of 90 (B. t. u./(hr.) (sq. ft.) (F. per ft.)) or better would be substantially as effective as magnesium,

The following table shows the improved yield of vitamin A concentrate from fish oil when a 4 inch aluminum rotor was used instead of a T 6 inch steel rotor. The tests of both aluminum and thin steel rotors were run in two 5-foot stills and the figures given are in each case the average for 3 clistillations.

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4 The ratio of the thickness to the diameter of the inch thick, 5 foot diameter aluminum rotor was thus 1/80.

The surface area was the same for both the steel and aluminum rotors used in the test but the aluminum rotor was thicker.

In concentrating vitamin A from fish oils on an aluminum rotor the loss is approximately 16% as opposed to a 33% loss on a steel rotor. Other improvements are decreased power consumption, less vibration, reduced and more uniform charring on the distillation surface, and easier cleaning. The concentrate is of improved quality and is sufficiently bland to use in margarine fortification.

What we claim is:

1. In a centrifugal vacuum still apparatus especially effective for distilling large volumes of thermally decomposable material, an aluminum rotor at least 30 inches in diameter and having a wall thickness in the region of the vaporizing surface at least of the diameter of the rotor, which thickness is substantially greater than the wall thickness necessary for structural strength.

2. In a high vacuum unobstructed path centrifugal still especially effective for distilling thermally decomposable material, an aluminum rotor having a diameter of 30 to 120 inches and a wall thickness in the region of the vaporizing surface of /120 to /60 the diameter of said rotor with the minimum thickness being not less than inch and the maximum thickness not more than 1 /2 inches, which wall thickness is substantially greater than the wall thickness necessary for structural strength of said rotor.

3. In a centrifugal vacuum still apparatus especia y effective for distilling thermally decomposable material, a cast aluminum rotor having a diameter not less than about 60 inches and a wall thickness in the region of the vaporizing surface of at least /120 the diameter of said rotor, which thickness is substantially greater than the wall thickness necessary for structural strength.

ERICK MCLEAN RUSSELL H. IVES.

REFERENCES CITED The following references are of record in the file of this patent:

High-Vacuum Short Path Distillation, by Hickman Chemical Review, vol. 34, No. 1, Feb. 1944, page 64,

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